Benzoyl peroxide is commonly used in topical pharmaceutical formulations to treat dermatologic conditions such as acne vulgaris, commonly referred to as acne. Topically applied antibiotics have also been used in topical formulations to treat dermatologic conditions such as acne. Examples of antibiotics that have been used topically to treat acne include macrolide antibiotic such as erythromycin and lincomycin-type antibiotics such as clindamycin and lincomycin.
Combination products containing benzoyl peroxide and an antibiotic have been utilized and provide increased anti-acne efficacy compared to formulations containing either benzoyl peroxide or an antibiotic alone. Klein, U.S. Pat. No. 4,497,794, discloses a combination formulation containing benzoyl peroxide and erythromycin for the treatment of acne. Compositions prepared generally as described in Klein '794 are marketed under the tradename Benzamycin® (Dermik Laboratories, Berwyn, Pa.). Combinations of benzoyl peroxide and lincomycin family antibiotics such as clindamycin are disclosed in Klein, U.S. Pat. No. 5,767,098, Baroody, U.S. Pat. No. 5,733,886, and Stiefel U.S. Pat. No. 5,466,446. Compositions prepared generally as described in Klein '098 are marketed under the tradename Benzaclin® (Dermik Laboratories) and as described in Stiefel are marketed under the tradename Duac® (Stiefel Laboratories, Inc., Coral Gables, Fla.).
One of the problems associated with topical therapy with compositions containing benzoyl peroxide, either alone or in combination with an antibiotic, is the localized irritation at the site of application. Benzoyl peroxide has been shown to have a concentration dependent irritation potential. See Mills et al, International Journal of Dermatology, 25(10):664-667 (1986) and Lassus, Current Medical Research and Opinion, 7(6):370-373 (1981). Each of the above products contains benzoyl peroxide at a concentration of 5% w/w, a concentration that is associated with irritation.
Benzoyl peroxide is practically insoluble in water. The irritation due to application of compositions containing benzoyl peroxide has been determined to be caused by the portion of the benzoyl peroxide that is in suspension, whereas dissolved benzoyl peroxide causes little or no skin irritation. See, Schwarz, U.S. Pat. No. 7,153,888; and De Villez, U.S. Pat. No. 4,923,900. Schwarz discloses a composition containing benzoyl peroxide wherein all of the benzoyl peroxide of the composition is in solution in an organic solvent. Because dissolution of benzoyl peroxide accelerates the degradation of benzoyl peroxide, Schwarz discloses that an antioxidant is included in the composition to improve the stability of the solution.
One disadvantage of Schwarz is that a high concentration of organic solvent is required in order to dissolve the benzoyl peroxide. High concentrations of organic solvents have a tendency to be irritating to skin, primarily due to the drying effect due to solubilization of skin lipids. In Tables 1 to 3, Schwarz discloses multiple examples of compositions containing various organic solvents and benzoyl peroxide. In each of the examples, the concentration of organic solvent is more than 10 times, and generally more than 15 times that of the benzoyl peroxide in the composition.
De Villez discloses a composition containing benzoyl peroxide, water, and a water-miscible organic solvent that is less volatile than water and in which the benzoyl peroxide is soluble. Prior to application on the skin, the benzoyl peroxide is in suspension in the composition. However, when applied to the skin, the water from the composition evaporates relatively rapidly compared to the organic solvent. The benzoyl peroxide of the composition is then dissolved in situ in the organic solvent, resulting in a solution of benzoyl peroxide after all of the water has evaporated.
In order for the De Villez composition to be transformed from a suspension to a solution, the composition must remain in residence on the skin surface for a sufficient time for the water in the composition to evaporate. During this time, the benzoyl peroxide is in suspension in the composition and the suspended particles are able to interact with the skin to cause irritation. Moreover, De Villez, like Schwarz, requires a relatively high concentration of an organic solvent, which may contribute to the irritation potential of such compositions.